This application claims the priority of Korean Patent Application No. 2002-62701, filed on Oct. 15, 2002, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an apparatus for generating inductively coupled plasma (ICP), and more particularly, to an ICP generating apparatus incorporating an antenna with a structure that can improve uniformity of plasma.
2. Description of the Related Art
Recently, plasma technology is widely used in the manufacture of semiconductor devices and flat display panels. Plasma is used for etching or depositing certain materials on the surfaces of wafers for fabricating semiconductor devices, or substrates for fabricating liquid crystal display (LCD) panels. Particularly, in etching or thin film deposition processes for manufacturing highly integrated semiconductor devices, the use of plasma equipment is increasing. Therefore, development of plasma generating apparatuses appropriate for etching, deposition, or other processes is important for the development of semiconductor manufacturing processes and equipment. The most important factors in the development of plasma equipment for semiconductor manufacturing processes are the capability to operate on large substrates in order to enhance production yield, and capability to perform processes for fabricating highly integrated devices. Specifically, in accordance with a recent increase in wafer size from 200 mm to 300 mm, enhancing uniformity of wafer treatment processes as well as keeping high plasma density have become very important.
Various types of plasma equipment have been used in conventional semiconductor manufacturing processes, e.g., a capacitive coupled plasma (CCP) type, an electron cyclotron resonance (ECR) type, a helicon type, an inductively coupled plasma (ICP) type, and a hybrid type combining two or more of the foregoing types. Among the various types of plasma equipment, the ICP type equipment is considered to be the best equipment for the 300 mm large-size wafers because the ICP equipment can generate plasma with high density and high uniformity and has a simple structure compared to the other types of plasma equipment. However, development of ICP equipment for 300 mm wafers is not easily achieved by simply changing the dimensions of existing ICP equipment for 200 mm wafers. There are plenty of limitations due to difficulties in designing antennas that are essential to ICP discharges.
FIG. 1 shows the structure of a conventional ICP generating apparatus. As shown in FIG. 1, the ICP generating apparatus includes a reaction chamber 10 including a space for generating plasma. An electrostatic chuck 12 for supporting a substrate, e.g., a wafer W, is provided at a lower portion within the reaction chamber 10, and a dielectric window 16 is formed in an upper cover 11 of the reaction chamber 10. A gas supply port 14 for supplying reaction gas into the reaction chamber 10 is formed at a sidewall of the reaction chamber 10, and a plurality of gas distribution ports 15 connected to the gas supply port 14 are provided within the reaction chamber 10. A vacuum suction port 18 is formed at the bottom of the reaction chamber 10 and connected to a vacuum pump 19 for evacuating the inside of the reaction chamber 10. Further, a coil antenna 20 for generating plasma within the reaction chamber 10 is provided above the dielectric window 16.
The coil antenna 20 is connected with a power source (not shown) for supplying radio frequency (RF) current. As the RF current flows in the coil antenna 20, a magnetic field is produced around the coil antenna 20, and in accordance with variation of the magnetic field as a function of time, an electric field is induced within the reaction chamber 10. At the same time, the reaction gas is supplied into the reaction chamber 10 through the gas distribution ports 15, and is ionized by collisions with electrons accelerated by the induced electric field to generate plasma within the reaction chamber 10. The generated plasma chemically reacts with the surface of the wafer W so that the wafer W is subject to a desired process, e.g., etching. Meanwhile, an additional RF power source (not shown) is generally connected to the electrostatic chuck 12 for supplying a bias voltage to increase the energy of ions derived from the plasma and collided with the wafer W.
FIG. 2 shows an example of a conventional spiral coil antenna, and FIGS. 3A and 3B show electric field distribution and density of plasma generated within the reaction chamber shown in FIG. 1 by the spiral coil antenna shown in FIG. 2, respectively. As shown in FIG. 2, the spiral coil antenna 30 is typically comprised of a single spirally wound conductive coil. However, the spiral coil antenna 30 has a disadvantage in that the intensity of the electric field induced thereby is not uniform. That is, as shown in FIG. 3a, the electric field is relatively weak at the edge portion of the spiral coil antenna, and is relatively strong at the center portion thereof. Therefore, the density of the plasma generated is lowest at the edge portion of the reaction chamber.
The most densely generated plasma at the center portion of the reaction chamber is diffused toward a wafer placed near the bottom of the reaction chamber. Consequently, the density of the plasma in an area near the wafer surface where reaction between the plasma and the wafer occurs is high at the center portion of the area near the wafer surface, and is low at the edge portion of the area near the wafer surface.
Such irregular plasma density distribution causes a problem of the depth to which the wafer or substrate is etched or the thickness to which a material is deposited on the wafer or substrate being non-uniform over the surface thereof. As the diameter of the reaction chamber is increased to accommodate larger wafers, this non-uniformity problem becomes more serious. Further, in order to keep the plasma density sufficiently high within the reaction chamber, the radius of the antenna 30 and the number of turns of the coil should be increased to conform to the increased size of the ICP equipment. However, increasing the number of turns of the coil causes another problem in that the self-inductance of the antenna increases, and accordingly, the efficiency of the plasma discharges is degraded. If the self-inductance of the antenna 30 increases, the antenna 30 requires a higher voltage, and capacitive coupling easily occurs. The capacitive coupling increases the kinetic energy of ions too high, thereby making it difficult to precisely control processes. In addition, as the ions with such high kinetic energy collide very strongly against the inner wall of the reaction chamber, undesirable particles are separated from the inner wall. Further, the capacitive coupling lowers the efficiency of the plasma discharges.
FIGS. 4A and 4B show the distribution of radial direction components of magnetic fields produced by a conventional circular coil antenna. The left photograph images in FIGS. 4A and 4B show the structure of the antenna as well as the distribution of the radial direction components Br of magnetic fields produced thereby, and the right graphs show the magnitude of the radial direction components Br of the magnetic fields as function of distance from the center of the antenna. In particular, the right graphs is the results of a simulation using Vector Fields, which is electromagnetic field analysis software, on the distribution of the radial direction components Br of the magnetic fields produced 5 cm below the center of the cross-section of the antenna coil, where current distributions in coils forming the antenna are assumed to be uniform across the entire cross-section of the coils.
The antenna shown in FIG. 4A includes three concentric coils having a radius of 7 cm, 14 cm, and 21 cm, respectively. Each coil has a 6×6 mm square cross-section. Current flows in the same direction through each coil.
When current flows in the same direction through each coil, the magnitude of the magnetic fields appear to be higher near the center portion of the antenna. Plasma generated at a strong magnetic field portion diffuses over the entire the reaction chamber. In a reaction chamber with such a magnetic field distribution, plasma density decreases from the center to the edge portion.
The antenna shown in FIG. 4B has the same structure as the antenna of FIG. 4A. However, current flows in opposite directions through adjacent coils. When current flows in opposite directions through adjacent coils as in the antenna of FIG. 4B, the inductance of the antenna drops by about 50% with respect to the inductance of the antenna of FIG. 4A, as illustrated in FIG. 13. However, due to a peak magnetic field intensity near the center of the antenna of FIG. 4B, it is unlikely to attain highly uniform plasma density.
FIGS. 5A through 5D show various antennas proposed to solve the problems of the above-described coil antennas. FIG. 5A shows an antenna 40 disclosed in U.S. Pat. No. 5,346,578, which includes a domed upper cover 44 for a reaction chamber 42, and a spiral coil wound around the upper cover 44 in dome shape. Advantageously, the geometry of the antenna 40 offers highly uniform plasma density.
However, it is difficult to manufacture such a domed upper cover 44, and the domed upper cover 44 is likely to suffer from stress to thermal expansion due to the antenna 40. In addition, because the coil is long enough to spirally wind the upper cover 44, from the upper portion to the lower portion, the inductance of the antenna 40 is increased. Accordingly, lower RF frequencies are required. For larger equipment manufactured to accommodate 300-mm wafers, the number of turns of the coil and the diameter of the antenna 40 increase. As a result, the above-described problems become more serious.
FIG. 5B shows an antenna 50 disclosed in U.S. Pat. No. 5,401,350, which includes a spiral coil antenna 50a formed on a top surface of a reaction chamber 52 and a solenoid type antenna 50b wound around an outer sidewall of the reaction chamber 52. The antenna 50 of FIG. 5B can compensate for the problem of low plasma density at the edge portion of a reaction chamber with the conventional spiral coil antenna described above. However, the antenna of FIG. 5B still has other problems with the conventional spiral coil antenna. Further, since the antenna of FIG. 5B requires two independent RF power sources, there are many process parameters to externally control. In practice, ICP generating apparatuses with the antenna of FIG. 5A or 5B utilizes considerably lower frequencies than a standard frequency of 13.56 MHz.
FIG. 5C shows an antenna 60 disclosed in U.S. Pat. No. 6,291,793, which includes a plurality of spiral coils 62, 64, and 66 branching off in parallel. The multiple and parallel type antenna shown in FIG. 5c is advantageous in that the self-inductance of the antenna 60 can be lowered as the number of branching off coils 62, 64, and 66 increases. However, such a multiple and parallel type antenna has no distinctive feature ensuring satisfactorily uniform plasma density distribution.
FIG. 5D shows an antenna 70 disclosed in U.S. Pat. No. 6,288,493, which includes a plurality of circular coils 71, 72, 73, and 74 branching off in parallel and a variable capacitor 76 connected to the plurality of circular coils to induce LC resonance between the circular coils 71, 72, 73, and 74. The antenna shown in FIG. 5D is advantageous in that highly uniform plasma density distribution can be achieved because the magnitude and phase of current are adjustable and that the inductance of the antenna is low due to the parallel structure. The antenna of FIG. 5D is regarded as the most advanced one among circular coil type antennas developed so far. However, if a LC resonance occurs between the parallel branching off antenna coils 71, 72, 73, and 74, an excess amount of current flows along the outermost coil 74 and arcing occurs at a point 75 from which the outermost coil 74 branches off.
Due to the problems described above, the conventional antennas disclosed so far have shortcomings in adequately conforming to variations in process conditions to obtain high plasma uniformity. Particularly, as wafers become larger, it is more difficult to maintain uniform plasma density near the edge portions of the wafers using the conventional antennas, and as a result, the quality and yield of semiconductor devices are seriously deteriorated.